More recently, however, increasing emphasis has been placed on including individual differences within a species—particularly behavioural traits—in seed dispersal studies (Zwolak and Sih 2020). Studies have shown that individuals within a population can differ consistently in their behaviour, which may influence the effectiveness of seed dispersal (Dall, Houston, and McNamara 2004; Wolf and Weissing 2012). For example, an animal’s personality—such as its boldness—can determine whether it acts as a seed predator or a seed disperser (Brehm and Mortelliti 2022).
Spotted nutcrackers (Nucifraga caryocatactes) are corvids that maintain a mutualistic relationship with the Swiss stone pine (Pinus cembra). In late summer, they harvest the ripe seeds and cache them in the ground as food reserves, thereby playing a key role in the regeneration of the tree species (Mattes 1982; Neuschulz et al. 2015). GPS tracking data from these birds make it possible to identify frequently visited locations and draw conclusions about individual harvesting and caching behaviours (Hertel et al. 2020; Auffret et al. 2017; Graf et al. 2024). The aim of this study is to analyse GPS movement data from individual spotted nutcrackers in the Swiss Alps to address the following research questions:
How do frequently visited sites differ between individuals, and can spatial clusters be identified?
Do visitation patterns differ between male and female birds in terms of their spatial distribution?
Material and Methods
Study Area
Both studies (Sorensen et al. 2022; Graf et al. 2024) tracked spotted nutcracker movements in 2017 and 2018 within a ~15 km² area around Davos in the eastern Swiss Alps (Figure 1). In this region, Swiss stone pine (Pinus cembra) forms the upper treeline between 1850 and 2200 m a.s.l., with the highest densities at mid-elevations. Valley bottoms are dominated by Norway spruce (Picea abies) and European larch (Larix decidua), where Swiss stone pine is scarce.